JPH0543209B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spectrum display device for an input signal of a receiver, and more particularly to a sweep signal oscillation means in the spectrum display device for an input signal.

[Conventional technology and its issues]

Bandscopes, spectrum analyzers, and the like are devices that can display the radio wave status of a specific band as a spectrum. FIG. 2 is a block diagram showing the basic configuration of the bandscope (spectrum analyzer).

The sawtooth sweep signal oscillated from the sweep signal oscillation means 1 is input to the local oscillation means 3, where it is input to the mixer 41 as a local oscillation signal that changes according to the voltage change of the sawtooth sweep signal. A signal to be displayed as a spectrum, such as a receiver input signal, is input to this mixer 41, and a signal having a frequency that is the sum or difference between the frequency of this input signal and the frequency of the local oscillation signal is obtained. The output of this mixer 41 is input to a filter 43 via an amplifier 42, where an intermediate frequency signal having a constant frequency defined by the filter 43 is obtained. This intermediate frequency signal is input to the vertical axis of the display screen of the display means 45 via the detector 44 and the like.

On the other hand, the sweep signal is inputted onto the horizontal axis of the display screen of the display means 45, thereby making it possible to display a spectrum on the display screen, with the horizontal axis representing the frequency and the vertical axis representing the intensity of the input signal. can.

In the above configuration, it may be necessary to change the frequency range (span) of the displayed spectrum. Therefore, as shown in FIG. 3a, the span adjustment means 2 is constructed by providing a variable resistor provided at the front stage of the DC amplifier. It may also be necessary to change or adjust the center frequency of the displayed spectrum (usually centered on the display screen of the display means). This center frequency is
Since it is determined by the bias voltage of the local oscillation means 3, a variable resistor is used as the bias setting means 32 of the local oscillation means 3.

Furthermore, FIG. 5a shows an equivalent circuit of the circuit shown in FIG. 3a above, and FIG. 5b shows the relationship between the maximum value V _Max , the minimum value V _Mio , and the center voltage _VO of the sweep signal. It is. The resistance value of the bias setting means 32 of the local oscillation means 3 is R _B , its bias voltage (voltage across the bias resistor) is V _B , the resistance value of the span adjustment means 2 is R _s , and the instantaneous sweep signal oscillator output When the voltage is V, the voltage V _A at point A, which is the input terminal of the bias voltage of the local oscillation means 3, is V _A = (V - V _B ) x R _B / R _B + R _S + V _B V _AMax = (V _Max −V _B )×R _B /R _B +R _S +V _B V _AMio = (V _Mio −V _B )×R _B /R _B +R _S +V _B Therefore, the maximum voltage at point A V _AMax and the minimum voltage at point A
The difference between the two voltages V _AMio is, if the resistance value R _B of the bias adjustment means 32 and the bias voltage V _B are constant,
When the span adjustment resistance R _s increases, it takes a small value,
When it decreases, it takes on a large value and depends on the span adjustment resistance R _s .

The voltage at point A, which determines the left and right center positions on the display screen, is the center voltage _AAO of V _A : V _AO = V _AMax + V _AMio /2 = {(V _Max + V _Mio −2V _B ) (R _B
/R _B +R _S ) +2V _B }/2 Here, since V _Max +V _Mio /2=V _O , (where, V _O : center voltage of the sweep signal (voltage V) ∴V _AO = (V _O −V _B ) (R _B /R _B +R _S )+V _B ...(1) Therefore, the voltage V _AO that determines the left and right center position on the display screen is the resistance value R _B of the bias setting means 32 and the bias voltage V _B If is constant, span adjustment resistance
It will depend on R _S.

Therefore, with this configuration, when the span adjustment resistor R _S is changed to perform span adjustment, the center voltage V _AO at the above point A changes as the span changes.
As a result, the position of the center frequency of the spectrum displayed on the display screen of the display means (usually displayed at the left and right center positions on the display screen) changes, and the local oscillator 3 changes each time.
The bias voltage _VB (using a VCO) must be adjusted (by changing the bias resistance), which makes the operation extremely troublesome (see Figure 3).

In addition, if we try to eliminate this drawback, Fig. 3b
As shown in the figure, it is necessary to operate the span adjustment resistor and the bias adjustment resistor of the local oscillation means 3 in conjunction with each other, which has the drawback of complicating the configuration.

Furthermore, a circuit as shown in FIG. 4 has also been used in the past. In this configuration, the output of the DC amplifier is
Since only the AC component is input to the local oscillation means 3 via the capacitor C, the center voltage of the sweep signal input to the local oscillation means 3 changes as the span is adjusted, as described above. There's no fear. However, when span adjustment is performed by operating the variable resistor in front of the DC amplifier, the capacitor is It charges and discharges, temporarily changing the bias voltage of the local oscillation means 3, resulting in a shift in the center voltage of the intermediate frequency signal, that is, the center frequency displayed on the display. Furthermore, when the span is increased, the change in frequency per unit time is large, causing a delay in response of filters and the like, resulting in distortion on the screen. In order to prevent this distortion from occurring, it is necessary to lengthen the period of the sweep signal, but in this case, distortion occurs in the sweep signal and a display error occurs.

Incidentally, in recent years, in order to check the state of radio waves near the receiving frequency of the receiver, a band scope or a spectrum analyzer has been installed in the receiver. If a bandscope or spectrum analyzer related to the above configuration is installed in the receiver as is, in addition to operating the receiver,
In addition to the drawback that the troublesome adjustment work such as the span adjustment, period change, and center frequency adjustment is increased and becomes extremely troublesome, the problem of the display error described above is also brought into play.

[Means to solve the problem]

This invention was proposed in view of the above-mentioned conventional problems, and the center voltage does not change even if the span or period of the sweep signal is changed, so that the center frequency of the target band can be It is always located at the center of the display screen without any special operations, and
It is an object of the present invention to provide an input signal spectrum display device that does not cause display errors.

This invention has been proposed in view of the above-mentioned conventional circumstances, and employs the following means. That is, a sawtooth sweep signal oscillated from the sweep signal generating means is input to the local oscillation means, and a local oscillation signal having a frequency that changes in accordance with the voltage of the sawtooth sweep signal is obtained from the local oscillation means. , is input to a mixer, the mixer calculates the difference or sum of the frequency of the received signal and the frequency of the local oscillation signal, obtains an intermediate frequency signal of a predetermined frequency via a filter, and displays the intermediate frequency signal on a display means. By inputting the above-mentioned sweep signal into the vertical axis of the screen and the horizontal axis of the display screen of the display means, an input signal is generated that displays the frequency spectrum corresponding to the input signal with frequency on the horizontal axis and intensity on the vertical axis. In this spectrum display device, the center voltage (V _O ) of the sweep signal oscillated by the sweep signal generation means and the local oscillation means that determine the input frequency displayed at the center left and right on the display screen of the display means. center voltage setting means of the sweep signal generation means for setting the bias voltage (V _B ) to the same value; and span adjustment means inserted between the sweep signal generation means and the local oscillation means for adjusting the span of the sweep signal. It is equipped with the following.

With this configuration, the span and period of the sweep signal maintain independence with respect to the center voltage of the sweep signal, and even if the span or period is changed, the center voltage does not vary, making the operation simple. Furthermore, since no capacitor is used, there is no display error.

〔Example〕

FIG. 1 is a block circuit diagram showing one embodiment of the present invention. A sweep signal oscillation means 1 such as an A/D converter converts the output of a shift register or CPU (not shown) into a staircase wave corresponding to a sweep signal via an I/O terminal 11 to a differential amplifier 1.
2, and the positive terminal of the differential amplifier 12 is grounded via a center voltage setting means 5 for the sweep signal described below. The center voltage setting means 5 for the sweep signal is composed of a semi-fixed resistor 51, the resistance value of the semi-fixed resistor 51 corresponds to the center voltage of the sweep signal, and the center voltage is at least the same as that of the sweep signal oscillating means 1. At the output end, it is determined only by the value of this semi-fixed resistor 51, and is not influenced by other factors such as the period and span of the sweep signal.

The output of the sweep signal oscillation means 1 is a local oscillation means via a span adjustment means 2 for span adjustment.
It is designed to be input to VCO31. VCO
31 is provided with a bias resistor 32 as in the conventional case, and is adjusted to a value corresponding to the intermediate frequency of a receiver (not shown) or the like. Said span adjustment means 2
has a switching resistor structure, and each resistor constituting the switching resistor is a semi-fixed resistor. Therefore, as will be explained below, by adjusting the value of each semi-fixed resistor, it is possible to determine the span of the sweep signal corresponding to the frequency of the desired display bandwidth.

From equation (1) above, the center voltage V _O of the sweep signal is made to match the bias voltage V _B of the local oscillator 3 (V _O =
V _B ), V _AO = V _B and no longer depends on R _S ,
Therefore, span adjustment will not affect the location of the center frequency.

That is, in the above configuration, the semi-fixed resistor 51, which is the center voltage setting means for the sweep signal signal, is adjusted so that the center voltage of the sweep signal matches the bias voltage of the local oscillation means 1. This work can be done, for example, by adjusting the resistance value of the semi-fixed resistor 51 to a value that does not cause the center frequency on the display to shift left or right when the resistance value is changed by operating the span adjustment means 2. . Conversely, when the adjustment is made as described above, even if the span of the sweep signal is changed by switching the resistance of the span adjustment means 2, the center voltage of the sweep signal will not fluctuate, and therefore the display frequency band will not change. The center frequency does not move left or right on the screen. Furthermore, the period can be changed by changing the input clock frequency to the shift register, or by changing the input clock frequency to the shift register.
Although this is done by the CPU, since changing the cycle does not affect the center voltage of the sweep signal, there is no need to adjust the semi-fixed resistor 51, which is the means for setting the center voltage of the sweep signal, in this case as well. There is no change in the center voltage. The above is an explanation of the case where a digital signal is used on the input side of the sweep signal oscillation means 1, but even with a purely analog sweep signal oscillation means, the center voltage setting can be changed by the span setting or the period. This can be realized as long as a circuit that can perform this independently of the settings of is used.

〔Effect of the invention〕

As explained above, in this invention, the center voltage of the sweep signal can be set regardless of the period and span of the sweep signal, so the period and span of the sweep signal oscillation means can be set. Even if changed, the center voltage will not fluctuate,
The set center frequency is always located at the center of the display screen without any troublesome adjustment work. Therefore, if this spectrum display device is applied to a receiver, there will be fewer troublesome operations other than the reception operation, which is convenient. Furthermore, since no capacitor is used, there is no display error caused by distortion of the sweep signal that occurs immediately after changing the span or when the period is increased.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram showing one embodiment of the present invention, Fig. 2 is a block diagram showing an outline of a band scope, etc., Fig. 3 is a block circuit diagram of a conventional spectrum analyzer, etc., and Fig. 4 is also a block diagram of a conventional spectrum analyzer. This is an example of a block circuit diagram of a spectrum analyzer, etc., and FIG. 5 is an equivalent circuit diagram and a sweep signal waveform diagram of the circuit shown in FIG. 3a. In the figure, 1: sweep signal oscillation means, 2: span adjustment means, 3: local oscillation means, 5: sweep signal center voltage setting means.

Claims (1)

[Scope of Claims] 1. A sawtooth sweep signal oscillated from the sweep signal generating means is input to the local oscillation means, and from the local oscillation means a local signal of a frequency that changes in accordance with the voltage of the sawtooth sweep signal is transmitted from the local oscillation means. Obtain an oscillation signal, input it to a mixer, calculate the difference or sum of the frequency of the received signal and the frequency of the local oscillation signal, pass through a filter to obtain an intermediate frequency signal of a predetermined frequency, and convert the intermediate frequency signal into By inputting the above-mentioned sweep signal to the vertical axis of the display screen of the display means and the horizontal axis of the display screen of the display means, the frequency spectrum corresponding to the input signal can be expressed as the frequency spectrum on the horizontal axis and the intensity on the vertical axis. In a spectrum display device for an input signal that is _displayed as center voltage setting means for the sweep signal generation means that sets the bias voltage (V _B ) of the local oscillation means to the same value; 1. A spectrum display device for an input signal, comprising: span adjustment means for adjusting.